The present invention relates of electrostatically transferring a toner image formed on a photoreceptor onto a recording sheet, specifically to a recording sheet guiding member used for an image forming apparatus such as a copying machine, a printer and a facsimile in which an electrophotographic method is applied and an image forming apparatus having aforesaid recording sheet guiding member.
Heretofore, as an image forming apparatus, a copying machine, a printer and a facsimile to which the electrophotographic method is applied are applied. Specifically, a constitution in which a visible image is formed by a process including a step to electrostatically transfer a toner image formed on a photoreceptor onto a recording sheet is widely used.
Practically, in an image forming apparatus to which the electrophotographic method is applied, the surface of the photoreceptor is charged by means of a charger. Using image exposure, an electrostatic latent image is formed. Aforesaid latent image is developed by a developer composed of toner for forming toner image. Under a status in which a recording sheet composed of paper is brought into contact with aforesaid photoreceptor drum retaining toner image, due to corona discharging having an opposite polarity with toner in a corona discharger for transferring, the toner image is caused to be transferred onto the recording sheet electrostatically. Further, due to corona discharge by a corona discharger for separation, the recording sheet having the toner image is electrostatically separated. By fixing the toner image onto the recording sheet separated, the visible image is formed.
In an image forming apparatus provided with a corona discharger for transferring toner image or for separating recording sheet, it is necessary to locate a recording sheet guiding member for conveying the recording sheet along a prescribed conveyance path. Due to this, erroneous advancement of the recording sheet is prevented. For example, collision of aforesaid recording sheet to a corona discharger body, hindering a prescribed conveyance, is prevented.
Incidentally, a recording sheet guiding member used for an image forming apparatus is ordinarily formed by an electrical insulating resin. Therefore, aforesaid guiding member is subjected to friction charging due to oscillation of aforesaid recording sheet when guiding it. Aforesaid charging potential may reach the maximum kV. Due to this, disturbance may occur on the toner image retained electrostatically onto the recording sheet.
When the guiding member is charged due to friction with the recording sheet, the status of the friction charging of the guiding member, for example, the polarity and the size of the charging potential may become abnormal, due to the kind of aforesaid recording sheet, characteristics of toner, environmental conditions, conditions of corona discharge and other reasons. In such occasions, if the charging polarity of the guiding member has the same polarity as the toner, the toner on the recording sheet is repelled due to the effects so that aforesaid toner is split off from the recording sheet. As a result, a part of image to be formed is missed. On the other hand, if the charging polarity of the guiding member is opposite to that of the toner, the toner is absorbed from the vicinity of the recording sheet. As a result, image portions which should not be formed or contamination are formed.
In order to solve the above-mentioned problems, Japanese Tokkaihei 4-301870 proposes to use a resin which is subjected to friction charging to an opposite polarity as the toner.
However, due to aforesaid means, the guiding member is caused to be charged due to friction. Therefore, if the guiding member is charged to the same polarity as the toner, the transfer charge on the rear surface of the recording sheet is offset to be extinguished. Since the toner is drawn to the ambient portion thereof, the toner of aforesaid portion becomes so thin that white streak (image clearness) occurs. On the other hand, if the guiding member is charged to the opposite polarity of the toner, the transfer charge on the surface of the recording sheet becomes noticeable. Therefore, the toner is collected to cause black streak. Finally, the above-mentioned problems cannot necessarily be solved surely. In addition, the kind of the material usable as the recording sheet guiding member is restricted. Accordingly, those having sufficient properties cannot be obtained necessarily.
Japanese Tokkaihei 1-304480 discloses to provide a conductive material in the recording sheet guiding member or to provide a conductive layer.
However, in aforesaid means, under high humidity, corona charge on the surface of the recording sheet is leaked. Therefore, the toner moves to the ambient portion so that white,streak occurs. On the contrary, under low humidity, the toner is subjected to friction charging, occurring white streak or black streak. As a result, under high humidity and low humidity, it is impossible to obtain those causing white streak or black streak. There occurs a problem that sufficient environmental suitability and durability cannot be obtained necessarily.
As described above, conventional recording sheet guiding members may disturb a toner image retained electrostatically on a recording sheet charged due to friction with a recording sheet. In addition, sufficient environmental suitability and durability cannot be obtained.